linux-kernel - Re: [PATCH] atmel_lcdfb: suspend/resume support

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Message-ID: <20080313210012.5b9b97c5@siona.local>
Date:	Thu, 13 Mar 2008 21:00:12 +0100
From:	Haavard Skinnemoen <haavard.skinnemoen@...el.com>
To:	David Brownell <david-b@...bell.net>
Cc:	Nicolas Ferre <nicolas.ferre@...el.com>,
	linux-fbdev-devel@...ts.sourceforge.net,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	"Antonino A. Daplas" <adaplas@...il.com>,
	ARM Linux Mailing List 
	<linux-arm-kernel@...ts.arm.linux.org.uk>,
	Sedji GAOUAOU <sedji.gaouaou@...el.com>,
	Patrice VILCHEZ <patrice.vilchez@...el.com>,
	Andrew Victor <linux@...im.org.za>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] atmel_lcdfb: suspend/resume support

On Thu, 13 Mar 2008 11:19:37 -0800
David Brownell <david-b@...bell.net> wrote:

> On Thursday 13 March 2008, Haavard Skinnemoen wrote:
> 
> > > +	sinfo->saved_lcdcon = lcdc_readl(sinfo, ATMEL_LCDC_CONTRAST_VAL);
> > 
> > You're saving CONTRAST_VAL into a field called saved_lcdcon even though
> > it has nothing to do with LCDCON1 or LCDCON2...
> 
> Yeah, why don't registers named LCDCONx have nothing
> to do with LCD CONtrast?  Better to have named the PWM
> registers PWM ... and say they could be used for either
> contrast or backlight control.

While I admit you have a point, I think it's easier to change the name
of that field than changing the hardware documentation at this point ;)

> The saved contrast/backlight counter value CONTRAST_VAL is
> one of two PWM control registers.

I know.

> > > +	lcdc_writel(sinfo, ATMEL_LCDC_CONTRAST_CTR, 0);
> > 
> > ...then you're altering CONTRAST_CTR...
> 
> That's forces the contrast signal low and disables the
> PWM counter, so it won't "randomly" leave the PWM output
> high when the clock is stopped (leaving at least some
> displays lit during suspend).

I'm not saying it's the wrong thing to do. I just think it's strange
that you alter a different register than the one you saved.

> It's possible that only CTR needed to be saved; all the
> backlight support in this driver still needs work.

Yes, I do think we can assume VAL stays unchanged during suspend.

> > > +}
> > > +
> > > +static int atmel_lcdfb_resume(struct platform_device *pdev)
> > > +{
> > 
> > > +	lcdc_writel(sinfo, ATMEL_LCDC_CONTRAST_CTR, sinfo->saved_lcdcon);
> > 
> > ...and later restoring the saved value of CONTRAST_VAL into CONTRAST_CTR.
> > 
> > Confused.
> 
> Yeah, that looks wrong; the patch below makes more sense.
> Though it *does* behave right for some reason...

Yes, that looks better. Perhaps you used a contrast value that happened
to set the right bits when written to CTR?

I still think the name of the saved_lcdcon field is confusing though.

Haavard
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